The present invention relates in general to transistor structures and, more particularly, to improved transistor structures, their uses and methods for making them wherein an insulated conductive gate spacer or an insulated conductive portion of a gate spacer is contacted and driven separately from the gate.
The use of lightly doped drain (LDD) regions in very large scale integrated (VLSI) metal oxide semiconductor (MOS) integrated circuit structures is well known to overcome electric field effects near the drain region which can cause short channel effects, punchthrough and hot carrier degradation. The formation of such LDD regions between the channel and the more heavily and deeper doped conventional drain region spreads out the electric field which mitigates short-channel effects, reduces hot carrier generation and increases the punchthrough breakdown voltage.
Spacers formed on the sidewalls of the gate electrodes of MOS transistors have been utilized in the formation of LDD regions. Both electrically nonconducting, typically oxide, spacers and electrically conducting spacers have been used; however, the spacers normally are not connected to a defined potential such that they float within the MOS structure including the transistors. When conductive spacers have been used for operation of an MOS transistor, they have served as an extension of the gate-electrode upon which they are formed.
While LDD transistors are an improvement over conventional MOS transistors, LDD transistors also have disadvantages in their own right. For example, transistor drive current is reduced in LDD transistors due to the transistor series resistance of the LDD regions.
Accordingly, there is an ongoing need for improved transistor structures which can be used to improve various characteristics of standard LDD transistors, for example, the transistor drive current and gate delays of logic circuits including the improved transistors. Preferably, the improved transistors could be used together with or in place of conventional transistors and/or standard LDD transistors in an integrated circuit. Such an improved transistor structure should provide higher breakdown voltage from drain to source side (BVDSS) and higher subthreshold voltages.